1. Field of the Invention
The invention relates to an abnormality diagnosing system for an internal combustion engine including a first fuel injection valve for injecting fuel into a cylinder, a second fuel injection valve for injecting fuel into an intake passage, and a control device that controls an injection pattern of the first fuel injection valve and the second fuel injection value. The control device stores engine operating conditions, such as the engine speed, engine load and the engine coolant temperature, when an abnormality occurs in the internal combustion engine, and makes a return-to-normal determination as to whether the engine returns to a normal operating state, under engine operating conditions that are the same as or within predetermined ranges of the stored engine operating conditions.
2. Description of the Related Art
One type of internal combustion engine includes an intake passage fuel injector for injecting fuel into an intake passage, and an in-cylinder fuel injector for injecting fuel into a combustion chamber of each cylinder. The internal combustion engine of this type changes an injection ratio between the injection amount of the intake passage fuel injector and that of the in-cylinder fuel injector, according to engine operating conditions of the engine load and the engine speed (see, for example, Japanese Patent Application Publication No. 2006-258031 (JP-A-2006-258031)).
In some cases, the internal combustion engine of the above type is provided with an abnormality diagnosing system for detecting, for example, an abnormality in a fuel system, and determining whether the fuel system that has been determined as abnormal returns to a normal operating state. More specifically, the abnormality diagnosing system stores the engine speed, engine load and the water temperature as engine operating conditions acquired when an abnormality in the fuel system is detected, and determines whether the fuel system or the engine returns to a normal operating state only when similar engine operating conditions are established.
However, when three injection patterns, i.e., an injection pattern using only the intake passage fuel injector, an injection pattern using only the in-cylinder fuel injector, and an injection pattern using both of the intake passage fuel injector and the in-cylinder fuel injector, are selectively used under the same engine operating conditions, for example, an erroneous determination as to whether the engine or fuel system returns to a normal operating state may be made based on the above-described engine operating conditions. More specifically, when an abnormality occurs in the fuel system under certain engine operating conditions, in the injection pattern using only the intake passage fuel injector, it may be determined that the engine or fuel system returns to a normal operating state under the same engine operating conditions, in the injection pattern using only the in-cylinder fuel injector. In this case, even though the abnormality in the fuel system occurs due to the use of the intake passage fuel injector, a diagnosis of the abnormality is conducted when the engine operates in the injection pattern using only the in-cylinder fuel injector; therefore, the abnormality diagnosing system may erroneously determine that the engine or fuel system returns to a normal operating state, in other words, the system may re-evaluate the engine or fuel system as normal. Similarly, the problem as described above occurs in a diagnosis of an abnormality, such as misfiring, other than the diagnosis of the abnormality in the fuel system as described above.